This invention relates to an adjustable lock for a rotary drive such as the drive of a screwdown valve or gate valve.
A publication entitled Sempell KB 440 180 DE discloses a lock for a stop valve wherein the extreme axial positions of an axially-movable, screw-threaded ring represent open and closed positions of the valve. A cylinder lock is disposed such that the lock bolt when extended engages the screw-threaded ring and prevents the same from moving axially, so that the valve is locked in one of the extreme positions. A second lock cylinder is located to enable the valve to be locked in the other extreme position such that it may be secured in either its open or closed position, but the lock positions are not adjustable.
German Utility Model 7 819 582 discloses a locking system for gate valves having a rising spindle wherein, since the lift is considerably greater than with a screwdown valve, a coaxial cylindrical sleeve is rigidly secured to the handwheel and the spindle extending therethrough is correspondingly elongated. Locking elements are secured in a desired number to the sleeve and lock bolts are engageable in a groove or recess formed in the elongated spindle.
A locking system of this kind is also known for short-movement screwdown valves having a rising valve spindle wherein a cylindrical lock member comprises a cylinder and a radially-extending lock bolt. The lock member is connected to the end face of the spindle which extends through the handwheel and is devised such that a cooperating recess in the handwheel extends all or some of the way around the lock member. When in the locking position, the lock bolt engages a groove in the handwheel recess or is disposed, when locking the valve spindle in the top end position, above the top edge of the handwheel. The usual practice for locks of this kind is to use cylinder locks whose key can be withdrawn only when the lock is in a desired locking position.
One of the unsatisfactory features of known locking systems is that the locking positions are preset and cannot be readjusted without considerable work. For instance, the lock of a valve which is lockable in the open position cannot be readily adjusted for locking thereof in the closed position or vice versa. Other disadvantages of prior locks arise because of the design limitations of the known locking systems of this kind. More particularly, due to the accumulation of manufacturing tolerances in long-production runs, considerable difference may arise between the actual locking position and the desired locking position of the present lock arrangements.